informal in WordNet English dictionary

1. having or fostering a warm or friendly and informal atmosphere
   "had a cozy chat"; "a relaxed informal manner"; "an intimate cocktail lounge"; "the small room was cozy and intimate"
   cozy  intimate  informal 
   
2. not formal
   "conservative people unaccustomed to informal dress"; "an informal free-and-easy manner"; "an informal gathering of friends"
   informal 
   
3. used of spoken and written language
   informal 
   
4. not officially recognized or controlled
   "an informal agreement"; "a loose organization of the local farmers"
   informal  loose